Burden of proof
Logically, there is no requirement for any particular set of rules regarding this, but there are good reasons for presuming the following:
- If a claim is questioned, supporters of that claim are obliged to defend it (i.e. the burden of proof is on the original assertion).
- From this derives the idea that extraordinary claims require extraordinary evidence -- in other words, any claim which goes sharply against common wisdom (i.e. the consensus belief) will require evidence of comparable magnitude in order to be taken seriously.
- Russell's teapot is often used as an example of burden of proof: if someone is claiming that there is an undetectable teapot in orbit between Mars and Jupiter, it is incumbent upon them to prove it -- rather than disbelievers being obliged to disprove it (which, in this case, be the notoriously difficult task of proving nonexistence).